Toxic effects to the nervous system may become detectable only after latent a period when the deficits become unmasked as a result of age-related degenerative processes. This hypothesis would take a long time to test in prospective studies, and retrospective assessment of prenatal exposure is bound to be seriously imprecise. This epidemiologic conundrum will now be resolved in the Faroe Islands, where prenatal exposure to methylmercury (MeHg) may be estimated, because the MeHg exposure primarily originated from ingestion of whale meat. Local catches of whale pods varied substantially between islands and from year to year, and dissemination of whale meat was difficult until about 1950, when more advanced transportation between the islands and refrigeration became available. A subject's potential exposure to MeHg prenatally can therefore be classified from the detailed whaling data for the pregnancy period at the place of birth. The Faroese have a very high intake of seafood, but their cardiovascular mortality is nonetheless higher than elsewhere in Scandinavia, and Parkinson's disease is about twice as common as expected. We will therefore examine two groups each consisting of about 250 men and women, who were all born around 1935, when variation in whale catches was the greatest. Matched by sex and age, one group's place of birth will be communities with great availability of whale, and the second group's place of birth will be communities without. Each subject will be approximately 70 years at the time of the study and will undergo a series of neurobehavioral and cardiovascular function tests. Postnatal exposure to MeHg and to polychlorinated biphenyls and related contaminants will be assessed by detailed questionnaire and by analysis of appropriate exposure biomarkers. In addition, essential nutrients from seafood, such as n-3 fatty acids and selenium will also be measured in blood samples. The effects of prenatal and/or postnatal neurotoxicant exposures will be determined after confounder control in statistical analyses that will include structural equation models. These results will provide evidence on long-term health implications of developmental and postnatal exposures to these neurotoxicants, which are widely present in freshwater fish and seafood, and the possible compensatory effects of concomitant intakes of essential nutrients. This study will provide unique evidence on adverse health effects of prenatal contaminant exposure as they appear at an advanced age. The results may therefore provide new information that could very likely have an impact on the preventive efforts and standard-setting of the EPA and other regulatory agencies in the U.S and elsewhere.